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First encounter effects in testing of highly automated vehicles during two experimental occasions – The need for recurrent testing

Jonas Andersson ORCID logo, Azra Habibovic and Daban Rizgary


To explore driver behavior in highly automated vehicles (HAVs), independent researchers are mainly conducting short experiments. This limits the ability to explore drivers’ behavioral changes over time, which is crucial when research has the intention to reveal human behavior beyond the first-time use. The current paper shows the methodological importance of repeated testing in experience and behavior related studies of HAVs. The study combined quantitative and qualitative data to capture effects of repeated interaction between drivers and HAVs. Each driver (n=8) participated in the experiment on two different occasions (∼90 minutes) with one-week interval. On both occasions, the drivers traveled approximately 40 km on a rural road at AstaZero proving grounds in Sweden and encountered various traffic situations. The participants could use automated driving (SAE level 4) or choose to drive manually. Examples of data collected include gaze behavior, perceived safety, as well as interviews and questionnaires capturing general impressions, trust and acceptance. The analysis shows that habituation effects were attenuated over time. The drivers went from being exhilarated on the first occasion, to a more neutral behavior on the second occasion. Furthermore, there were smaller variations in drivers’ self-assessed perceived safety on the second occasion, and drivers were faster to engage in non-driving related activities and become relaxed (e. g., they spent more time glancing off road and could focus more on non-driving related activities such as reading). These findings suggest that exposing drivers to HAVs on two (or more) successive occasions may provide more informative and realistic insights into driver behavior and experience as compared to only one occasion. Repeating an experiment on several occasions is of course a balance between the cost and added value, and future research should investigate in more detail which studies need to be repeated on several occasions and to what extent.


Funding source: VINNOVA

Award Identifier / Grant number: 2017-03058

Funding statement: The project was funded by SAFER Open Research at AstaZero (Grant No. A-0018), the VINNOVA Strategic Vehicle Research and Innovation program (project Trust in Intelligent Cars - Grant No. 2017-03058), and the Knowledge Foundation (project Action Intention Recognition - Grant No. 20140220)


We want to thank our colleagues Maria Klingegård, Alexey Voronov, David Lindström, Victor Malmsten-Lundgren and Emma Asker for their work at the AstaZero proving grounds, and with data analysis.

Appendix A

Table A.1

Scenarios at the test track demonstrating HAV capabilities.

RoadworksA static roadworks is marked by cones and a roadwork sign. It is visible from distance. The roadworks demonstrates that the HAV can handle zigzag driving
Upcoming & OvertakingThe HAV catches up a slow-moving vehicle (ca 40 km/h) in the same lane. The road section is straight, and visibility is good. The HAV decides to either follow the slow-moving vehicle (too short distance to intersection) or perform an overtake. This demonstrates that the HAV can handle overtaking
IntersectionA vehicle is about to enter the priority road (i. e. it should yield). Before entering it stops. To demonstrate that it has understood the situation and possible risk, the HAV slightly adapts its speed
Oncoming trafficThe HAV encounters a vehicle travelling in the adjacent lane in the opposite direction

Table A.2

The level of safety categorized into safe (i. e., TPs used the Swedish word “trygg” in their expression), and quite safe (i. e., TPs used expression such as “ganska trygg”). No stronger expression of uncertainty or unsafety were identified.

Test participantOverall safety – Occasion 1Progress over time during Occasion 1Overall safety – Occasion 2Progress over time during Occasion 2
TP2SafeIncreasen/aNo change
TP3Quite safen/aSafeIncrease
TP4Safen/aSafeNo change
TP5Quite safeNo changeSafen/a
TP6Quite safen/aQuite safen/a
TP7SafeIncreaseSafeDecrease, increased
TP8SafeNo changeSafe, quite safeNo change
TP9SafeNo changeSafeNo Change
Figure A.1 TPs’ answer to the post drive question “Would you feel safe to test the AD in real traffic?”

Figure A.1

TPs’ answer to the post drive question “Would you feel safe to test the AD in real traffic?”


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Received: 2020-07-10
Revised: 2021-03-21
Accepted: 2021-03-29
Published Online: 2021-04-10
Published in Print: 2021-06-25

© 2021 Walter de Gruyter GmbH, Berlin/Boston

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